YEAR-CLASS STRENGTH OF PIKEPERCH (STIZOSTEDION-LUCIOPERCA L) IN RELATION TO ENVIRONMENTAL-FACTORS IN A SHALLOW BALTIC-BAY

The effects of several environmental factors on the relative year-clas s strength variations of pikeperch (Stizostedion lucioperca (L.)) were studied in a shallow brackish Baltic bay in Helsinki, Finland, during 1971-1990. The year-class strength correlated positively with the mea n summer water temperature from June to September during the first yea r of life. Negative correlations between the year-class strength and w ind indices were found with the southerly and southwesterly winds in J uly. These winds explained 35% (F = 4.53, P = 0.027, n = 20) and the m ean temperature alone 40% (F = 9.89, P = 0.007, n = 17) of the total v ariation in year-class strength. When the exceptionally weak year-clas s in 1971 was excluded from the analysis, the corresponding values wer e 62% for the winds (F = 6.50, P = 0.007, n = 19) and 55% for the mean summer temperature alone (F = 16.92, P < 0.001, n = 16). No correlati on existed between the year-class strength and water level, water sali nity or water transparency.